1. Field of the Invention
The present invention relates to a method for filtering particles out of a beam of radiation propagating from a radiation source towards a processing system, a filter system, an apparatus and a lithographic apparatus including the filter system.
2. Description of the Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. including part of one or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning” direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
In order to be able to image smaller features, it has been proposed to use extreme ultraviolet radiation (EUV) with a wavelength in the range of 5 to 20 nm, particularly 13 nm, or a charged particle beam, e.g. an ion beam or an electron beam, as the exposure radiation in a lithographic apparatus. An example of an EUV radiation source is a laser plasma source. Plasma radiation sources, however, besides EUV radiation, often generate debris. Debris entering an illumination system and/or a projection lens should be entirely avoided or minimized.
U.S. Pat. No. 6,359,969, incorporated herein by reference, discloses a debris filter including a plurality of foils or plates, which foils or plates are arranged radially around the radiation source.
U.S. Patent Application Publication 2003/0020890 A1 discloses a debris removing system for preventing debris, originating from a radiation source, from entering an optical system. The debris removing system includes an attracting unit having an attracting surface approximately parallel to an axis passing through the radiation source. The debris removing system further includes a rotation unit for rotating the attracting unit about the axis. Part of the rotation unit blocks part of the radiation from entering the optical system, e.g. thus reducing the radiation transferring efficiency of the debris removing system Furthermore the attracting unit occupies a large volume close to the radiation source, so that placement of the debris removing system becomes difficult and/or the volume available for the radiation source is limited.